The invention relates to vehicles that have steered wheels on several axles, and in particular relates to the devices used to orientate the rear wheels.
Rear wheel orientation devices generally comprise a hydraulic or electric actuator. Such actuators have an actuating member the movements of which alter the angular orientation of the rear wheels about the vertical of the vehicle. The grease used to lubricate the bearings that guide the actuating member create resistance to movement which increases at low temperature. In the case of a hydraulic actuator, the viscosity of the hydraulic fluid used to move the actuating member also increases appreciably. The load on the hydraulic pump used to pump the hydraulic fluid then increases appreciably. What is more, the forces needed to alter the orientation of the rear wheels increase appreciably at low speed or when the vehicle is in reverse gear.
In order to detect malfunctions, a known wheel orientation device determines when the force that needs to be applied to the actuating member is too high and locks the wheels in their orientation. Further, this device commands the illumination of a warning lamp in the cabin recommending that the user stops the vehicle and goes to the nearest garage. Thus, a drop in temperature may cause a warning lamp such as this to light up in the cabin.
As a result, a user may find himself under temperature and running conditions in which the rear wheels are locked in a non-neutral orientation for the remainder of his journey (that is to say until the ignition is switched off), and this may disrupt driving conditions. What is meant by neutral orientation is a position in which the orientations of the rear wheels are symmetric with respect to the vehicle axle centerline. The user is also needlessly alarmed by a warning lamp even though the vehicle has not actually really broken down.